1. Field of the Invention
The present invention generally relates to interface circuits, and more particularly to an interface circuit capable of controlling a plurality of external circuits using at least one port, and an electronic device using the interface circuit.
2. Description of Related Art
Many electronic devices such as CD/DVD players, MP3 players, and mobile phones are widely used. Almost every such electronic device includes a plurality of input/output ports for communicating with other electronic devices such as earphones, keyboard, display, and so on.
Typically, as illustrated in FIG. 5, a traditional electronic device 10 includes a micro-processor unit (MPU) 100 provided with output ports 103, 105, and 107. The output ports 103, 105, 107 are connected to external circuits such as illuminating circuits 112, 114, and 116 respectively. The illuminating circuits 112, 114, and 116 have the same structure, just the illuminating circuit 112 will be explained as an example. The output port 103 is connected to the base of a transistor Q21 of the illuminating circuit 112. The collector of the first transistor Q21 is for receiving a 3.3 volts via a resistor R1 and a light-emitting diode (LED) D21. The emitter of the transistor Q21 is grounded. In order to drive the diode D21 to emit light, the MPU 100 outputs a high level voltage signal from the port 103 to the base of the transistor Q21 to turn on the transistor Q21. The output ports 105 and 107 are configured for driving the illuminating circuits 114 and 116 in a similar way. However, each of the illuminating circuits 112, 114, 116 must occupy a separate port.
Therefore, what is needed in the industry is to provide an interface circuit capable of using just one port to control a plurality of external circuits, and an electronic device using the interface circuit.